Oscillator and modulator



Dec. 29, 1936.

H. F. ELLIOTT OSCILLATOR AND MODULATOR .Filed April 21, 1932 Ham/d FI Elliott BY HIS ATTORNEY Patented Dec. 29, 1936 UNITED STATES PATENT OFFICE 12 Claims.

This invention relates to systems for producing oscillations and for carrying out the functions of modulation and de-modulation by means of electronic tubes. An object of my invention is to provide means whereby a single electron tube may be used for producing oscillations and at the same time perform the function of modulation or of de-modulation. Another object is to provide means whereby these various functions may be carried out in a single tube without detrimental reaction between the connected circuits. Another object is to provide means whereby the several functions may be carried out in an electron tube of simple construction and with simple circuits and equipment. Another object is to provide means whereby electronic amplifying and detecting apparatus such as a broadcast receiver may be simplified and reduced in size and cost.

Referring to the drawing:

Figures 1 and 2 show electron tubes which are adapted for carrying out the purposes of my invention.

Figure 3 shows a circuit for a complete superheterodyne type of receiver embodying the principles of my invention.

Figure 4 shows a second circuit arrangement by means of which the principles of my invention may be applied.

Referring to Fig. 1, numeral 2 designates a cathode which may be of the uni-potential type. Numeral 3 designates a connection to the cathode which may be brought out to a terminal on the'base of the tube. Numeral 4 designates a. heater wire within the cathode for raising the temperature of the latter to the level required for emission of electrons. Connections forthe heater are shown at 55. Numeral 6 designates an anode and numeral 1 a terminal for thesame brought out to a connection on the base. Numerals 8 and 9 designate two control grids symmetrically arranged in the space between the cathode and the anode. For the sake of clarity, one of these grids, as8, is shown in full lines, and the other, as 9, is shown in dotted lines. Numerals I0 and H designate terminals for the two grids, 8 and 3 respectively.

Figure 2 shows a second tube also suitable for 50 carrying out the objects of my invention. This tube is similar to that of Fig. 1 except that an additional electrode in the form of a screen grid 12 is placed between the control grids 8, 9 and the main anode 6. A connection for the screen grid is shown at I3.

Referring to Fig. 3, tube I4 is an amplifier arranged to amplify incoming signals at the frequency at which they are received. Tube l5 combines the functions of detection and production of oscillations and serves to heterodyne the incoming signals thereby converting them to an intermediate frequency where they are further amplified in tube 16. Tube ll is a second detector which serves to de-modulate the intermediate frequency signals and convert them to audiofrequency signals. Tube I 8 is an audio-frequency amplifier or power output tube which serves to amplify the audio-frequency signals and deliver them to speaker 19. Tube 29 is a rectifier which serves to supply direct current potentials of a few hundred volts for the operation of the aforementioned tubes and their circuits. Capacitors 2|, 2!, 2| together with chokes 22 and 23 serve to smooth the pulsations from the direct current delivered by rectifier tube 26. Inasmuch as all of the tubes except the two detectors l5 and I! may. be of standard construction and employ circuits substantially the same as are generally used in commercial superheterodyne receivers now on the market, only the connections and special features pertaining to tubes l5 and I! will be described in detail herein.

Tube I5 preferably takes the form of one of the tubes shown in Figs. 1 and 2. Either of these tubes may be used, the only difference between the two being that the tube of Fig. 2 includes a screen which gives it a high amplification factor and correspondingly high plate impedance.

In the circuits shown in Fig. 3, connections are provided for tube I5 whereby one grid, as 8, re-' 1 ceives radio frequency signals and the other grid 9 serves for the generation of oscillations. With this system of connections the tube acts as an autodyne detector-oscillator. Circuit 24 may be tuned to resonance at the frequency of the incoming signals and circuit 25 may be tuned to resonance at the heterodyning frequency which, as is well understood, may be either greater or less than the frequency of the incoming signals. In commercial broadcast receivers it is now common practice to make the heterodyning frequency approximately 175 kilocycles greater than the frequency of the incoming signals, thereby setting the operating period of the intermediate frequency amplifier at 175 kilocycles. circuit of tube !5 includes coils 26 and 21 which may betuned by capacitor 28 to'resonance at the intermediate frequency (for example, 175 kilocycles). Coil 26 may serve as the primary of an The output intermediate frequency transformer whose secondary is coil 29.

Coil 21 may serve as a feed-back coil for transferring energy from plate circuit of tube l5 to the grid circuit thereof for the purpose of producing and sustaining oscillations. Tube I5 is preferably constructed so that the capacitance between grid 8 and grid 9 is comparatively small, thereby minimizing any tendency toward interference between circuits 24 and 25. This condition is readily attained with commercial tubes so long as the resonants periods of circuits 24 and 25 are reasonably separated. The separation of 175 kilocycles employed in broadcast receivers of the superheterodyne type now in general use is quite satisfactory.

Tube |5 may be constructed as shown in either of the Figs. 1 and 2. The use of the screen grid i2, as shown in Fig. 2 and the diagram of Fig. 3, improves the sensitivity of the tube as a detector but is not essential. The choice of a tube with or without screen is dependent upon operating conditions and is not an essential element in my invention.

The second detector I1 is preferably, though not necessarily, arranged to utilize a tube of the type shown in Fig. 1. The two grids 8 and 9 may be connected to the opposite terminals of coil 30 which preferably has a center tap. A connection may be made from this center tap through resistors 3| and 32 to the cathode 2. Potentiometer 3233 serves to place a small initial positive bias on the grids 8 and 9 for the purpose of avoiding distortion due to grid currents or extraneous potentials induced on the grids. When signals are tuned in, tube ll functions as a grid leak detector with balanced input and grids 8 and 9 become negatively charged with respect to the cathode. This negative charge may be used for automatic volume control by feeding the negative potentials from the grids 8 and 9 back to the grid circuits of tubes I4 and I6. This may be carried out through the medium of resistor 34, bus 35 and capacitor 36. The output circuit of tube may contain either a resistor 31 as shown, or an iron core choke coil, or the primary of the suitable audio-frequency transformer. When resistor 31 is employed the audio-frequency output of tube may be fed to the succeeding amplifier tube |8 through the medium of coupling capacitor 38 and potentiometer 39. The latter may be provided with a sliding arm to serve as means for adjusting the input to tube I8 and thereby controlling the output from the speaker I9.

The choice of the values for the various resistors and capacitors will depend upon the constants of the various tubes employed and upon the potentials used in their operation. These choices are well understood by those conversant with vacuum tube operation and therefore need be given only approximately here. In general, with standtubes of the type now in commercial use, resistor 3| should be of the order of megohm; resistor 33 of the order of a megohm; resistor 32 about 10,000 ohms; resistor 34 about one megohm; resistor 31 about 100,000 ohms; potentiometer 39 about /2 megohm; by-pass capacitors 36, 38, 48 and 49 of the order of .05 microfarad. Biasing potentials for the grids of the various tubes may be obtained by any of the conventional means. For example, a resistor 39' of the order of a few thousand ohms may be included in the cathode circuit of tube I5 to supply biasing potentials for the grids thereof. 7

Capacitor 40 in the grid return circuit of tube may be of the order of 50 to micro-microfarads or may represent simply the stray capacitances of the circuits connected to resistor 3|.

Fig. 4 shows an alternative system of connections whereby tubes of the types shown in Figs. 1 and 2 may be utilized for producing oscillations and at the same time performing the functions of modulation or de-modulation. In Fig. 4, input signals from circuit 4| may be trans ferred by coupling to circuit 42. The latter may be tuned if desired and should be provided with a tap at its electrical center whereby the input signals may be applied to the two grids 8 and 9 of tube 43 in phase opposition. Potentials from circuit 44, which is used in the production of oscillations, should be applied to the two grids 8 and 9 in phase addition, as shown. The output circuit of tube 43 may include a coil 45 for transferring modulated or de-modulated signals to an. output circuit 46. The output circuit of tube 43 may also include a coil 41 to feed back energy from the anode to the grids for producing oscillations. The output circuit may include a source of anode potential, as battery 50, and the input circuit may include a source of biasing potential, as battery 5|; or alternatively, a grid leak and capacitor such as is shown at 3| and 40 in the grid circuit of tube Fig. 3, may be used. Still another alternative is the use in the grid circuit of a circuit tuned to resonance at the output frequency, i. e., a tuned grid leak.

The tubes of Figs. 1 and 2 and circuits of the type shown in Fig. 4 have a wide range of application as oscillators, modulators and de-modulators. For example, audio-frequency or radio frequency signals from the input circuit 4| may be used to modulate oscillations produced in circuit 4'! and the resultant signals delivered to out put circuit 46. As another example, signals consisting of a single side band from input circuit 4| may be de-modulated through the medium of oscillations supplied by circuit 41 and delivered as either audio-frequency signals or radio frequency signals to output circuit 46. A great variety of other uses may be made of the tubes and circuits. The invention, as defined in appended claims, is not limited to the arrangements described.

What I claim is:

1. A self oscillating frequency changer comprising. a single electron tube having a single cathode,'a single anode and two grids symmetrically proportioned and disposed relative to the cathode, and anode, an oscillator circuit in which the two grids serve in phase addition, and a signal circuit in which thetwo grids serve in phase opposition, the signal circuit comprising a center tapped impedance connected across the grids with a return circuit from the center tap to the cathode and the oscillator circuit comprising an impedance in the return circuit, feed back means coupling the anode and said impedance and a source of energy in an anode-cathode circuit.

2. In a radio receiver an oscillator-modulator comprising an electron tube having a cathode, an anode and two control grids of the same dimensions symmetrically spaced relative to the cathode and anode, a resonant circuit associated with each grid, said resonant circuits having different periods, a source of direct current, a feedback coil connecting the source, cathode and anode coupled to one of said resonant circuits, and a resonant circuit including an inductor and a capacitor in series bridged across the feed-back coil.

3. In combination, an electron tube having a;

cathode, an anode and two intermeshed control grids of like dimensions and positions relative to the cathode and anode, a resonant circuit for each control grid, means of applying signals to one circuit, a source of energy and feed-back means for causing oscillations to be produced in the other circuit, and a resonant output circuit comprising an inductor and a capacitor in series connected in parallel with the feed back means.

4. An apparatus as set forth in claim 2 with proviso that a screen grid be included in the electron tube and means biasing said screen grid relative to the cathode included in said circuits.

5. An apparatus as set forth in claim 3 with proviso that a screen grid be included in the electron tube and means biasing said screen grid relative to the cathode included in said circuits.

6. In a radio receiver with ganged tuning capacitors having a common rotor, a detectoroscillator comprising an electron tube having a cathode, an anode and two equal intermeshed and symmetrically disposed control grids, a tuned signal input circuit connecting the cathode and one grid, a tuned oscillation circuit connecting the cathode and the other grid, and a circuit comprising the cathode, anode, a source of potential an oscillation feed-back reactor coupled to the aforesaid tuned oscillation circuit and an output impedance comprising an inductor and a capacitor in series connected across the feed back reactor.

7. A receiver as in claim 6 with the addition of a screen grid in the electron tube and means biasing said screen grid relative to the cathode.

8. An apparatus as set forth in claim 1 with proviso that the two grids shall be intermeshed.

9. An oscillator-modulator comprising an electron tube having a single cathode, a single anode and two equal intermeshed grids symmetrically located relative to the cathode and anode, a balanced input circuit comprising equal impedances serially connecting the grids with a center tap connecting to a cathode return circuit for applying signals to the two grids in phase opposition, an oscillator circuit comprising an impedance in the cathode return circuit for generating oscillations with the two grids in phase addition, biasing means for the grids and an output circuit including a source of potential, the anode, the cathode, feed back means coupled to aforesaid tuned impedance and an output impedance.

10. An apparatus as set forth in claim 9 with the proviso that a screen grid be included in the electron tube and means biasing said screen grid relative to the cathode included in said circuits.

11. An oscillator-modulator comprising a single electron tube having a single cathode, a single anode and two equal, symmetrical, intermeshed control grids, an input circuit comprising impedances connected serially with the grids and forming an electrically balanced circuit therewith, a tap at a point of balance relative to the cathode and at least one tuned impedance connected between the tap and the cathode, and an output circuit comprising the anode, cathode, a source of potential and feed back means coupled to aforesaid tuned impedance.

12. A means of suppressing currents of input signal frequency in the output of an electronic oscillator-modulator having a cathode, an anode and two control grids which comprises means for applying input signal currents of equal value but opposing phase to the two grids, and means for balancing the control effect of input signal currents relative to space discharge electrons in said oscillator-modulator.

HAROLD F. ELLIOTT. 

